The Undulating Hills of Highway 195

As Wayne and I drove Highway 195 from Spokane to Pullman under cloudy skies, we were very interested in the geology of the area. There were a few hints, volcanic rock visible under the surface in the road cuts, and the smooth surface of the undulating hills rolling from horizon to horizon. I went online and here is a great article at the US Geological Survey website.

Eruptions 30 to 10 million years ago covered a vast area including parts of Idaho, Washington and Oregon with molten lava. Subsequent tilting and folding, and the deposit of wind blown silt (loess) and ash over the surface gave this wheat growing region the beginning of its fertile soil.

Glacial ice fields with melt lakes at their bases encroached on the area about 100,000 years ago. Lake Spokane covered what is now the city and much more. Massive Lake Missoula to the east filled beyond the capacity its ice dam. The resulting flood of catastrophic proportions flooded west towards the Pacific, scouring the surface down to the volcanic basalt, creating the water eroded channeled Scablands to the west. - Margy